In a commercial physical vapor deposition (PVD) system, the lifetime of a sputtering target is usually designed by the original equipment manufacturer (OEM). Such a lifetime, usually defined as a sputtering power times sputtering time (kilowatt-hours) or as the total thickness of material deposited on the substrates (microns, or number of 1 micron depositions), is mainly determined by the sputtering target material, target geometry and cathode magnet design. The sputtering cathode assembly is optimized for its performance parameters, such as deposition uniformity for the given design.
Target uniformity performance is determined mainly by the following three factors: the erosion profiles of the target during sputtering, target crystallographic texture, substrate to target distance, and the gas scattering factor during the deposition process. The erosion profile is the most important factor in determining the deposition uniformity. It also remains largely unchanged for a given PVD system.
In a PVD process, a cloud of plasma is present in front of the sputtering target. This plasma is sustained by the magnetic field from the magnets behind the sputtering target. The density of the plasma and, hence, the rate of sputtering of the target is related to the magnetic field strength at the target surface. Electrical-magnetic theory indicates that the maximum sputtering rate occurs when the vertical component of the magnetic field is zero and the horizontal component of the magnetic field is at maximum. In the following, the term “magnetic field” refers to the horizontal component of the magnetic field when the vertical magnetic field is near zero if it is not otherwise indicated.
In an advanced magnetron PVD design, the cathode magnet usually consists of an array of small magnets rotating around a target center axis to give better uniformity performance. At different locations on the target surface the magnetic field strength and the average residence time of the magnetic field per revolution of the magnets vary. Both of these variations contribute to the existence of different sputtering rates at different locations on the target surface, hence the existence of the target sputtering profile (sputtering grooves). We define the time integration of the magnetic field strength within a revolution as time averaged magnetic field strength (T-B-Field). In a commercial PVD system, the OEM usually designs the configuration of the cathode magnet assembly to form the desired T-B-Field. This, in turn, creates the desired target surface erosion profile that is adapted to achieve optimal deposition uniformity performance. Methods for determining desired magnet configuration and target erosion profiles may be seen upon review of U.S. Pat. Nos. 4,995,958; 5,314,597; 5,248,402; 5,830,327; and 5,252,194.